Capacitive touch panel sensors include touchscreens or touch panels comprising arrays of sensing cells. Touches cause capacitance change at the cell or cells underlying the region being touched. The touchscreen controller detects and locates the capacitance changes by analyzing signals generated by the cells due to capacitance change, the signals undergoing analog amplification and filtering followed by digitization and subsequent digital signal processing. The primary result of the analysis is the determination of the affected cell position and hence, the corresponding touch location.
However, the cells in any given array may vary widely in their capacitance values. This intrinsic variation, combined with variation in the characteristics of analog amplification components, power supply variations and other factors can cause the signal amplitudes output by the cells to vary through a dynamic range of up to 20 dB. Such a large variation complicates the determination of touch position. Approaches such as applying a global signal threshold to distinguish between touch and no-touch states have been discovered to be of limited value.
What is needed is a touchscreen system, and method of operating such a system, that can equalize the effective gain of each individual cell of a touch panel sensor without causing deterioration in the sensor's ability to track touches of interest.